The specific aims and objectives of the project are: A. To conduct 4, 5, and 6 year clinical evaluations of 500 dental amalgam restorations made from six representative spherical, lathe-cut and dispersion type alloys. B. To determine strengths and weaknesses of the three evaluation systems used by comparison of ranking data obtained by each method, using various statistical methods of analysis. C. To characterize, in vitro, the chemical, mechanical, and corrosion properties of the amalgams as used in the clinical studies at University of the Pacific and at Oral Roberts University. D. To determine a predictive model for amalgam deterioration in vivo, based upon the characteristics developed in the vitro tests and the clinical behavior of the amalgams. E. To suggest a design for future clinical research on Dental Amalgam (sample size; methods of evaluation and analysis; controls). Objectives A and B will be carried out jointly between UOP and ORU (Ryge, Tonn, Jendresen, Eick). Three evaluation systems will be employed: 1) Direct clinical evaluation according to rating system and criteria developed by Ryge, et al., 2) Visual assessment of occlusal photographs as proposed by Mahler, et al., and 3) Stereophotogrammetric method developed by Eick, et al. Objective C will be carried out at Georgia Institute of Technology by Drs. Hochman and Marek. The corrosion tests will include determination of anodic polarization behavior and corrosion potential measurements in synthetic saliva, constant potential coulometric tests in 1% sodium chloride, and corrosion current measurements using linear polarization techniques. Also crevice corrosion tests to evaluate pH drop will be carried out. Objective D will involve all professional personnel under the direction of Dr. Ryge. This is a competing renewal application for NIH Grant DE 04516.